Leishmania mexicana: Molecular cloning and characterization of enolase

High-confidence glycosomal membrane protein inventory unveils trypanosomal peroxin PEX15

Trypanosomatid parasite infections cause Chagas disease, human African trypanosomiasis, and leishmaniasis, affecting over 12 million people worldwide. Glycosomes, the peroxisome-related organelles of trypanosomes, are essential for survival, making their metabolic functions and biogenesis mediated by peroxins (PEXs) suitable drug targets. We report a comprehensive protein inventory of glycosomal membranes, defined through advanced subcellular membrane protein profiling combined with quantitative mass spectrometry and including 28 high-confidence glycosomal membrane proteins. We validate four previously unknown glycosomal membrane proteins, including a tail-anchored protein, which we show to be the long-sought Trypanosoma PEX15. Despite low sequence similarity, Trypanosoma PEX15 exhibits structural and topological similarities with its yeast and human counterparts, and it is essential for glycosome biogenesis and parasite survival. Considering the low degree of conservation with its human counterpart, PEX15 is a promising target for drug development. This inventory is an important resource for characterizing glycosome biology and therapeutic development.

Exploring glycolytic enzymes in disease: potential biomarkers and therapeutic targets in neurodegeneration, cancer and parasitic infections

Glycolysis, present in most organisms, is evolutionarily one of the oldest metabolic pathways. It has great relevance at a physiological level because it is responsible for generating ATP in the cell through the conversion of glucose into pyruvate and reducing nicotinamide adenine dinucleotide (NADH) (that may be fed into the electron chain in the mitochondria to produce additional ATP by oxidative phosphorylation), as well as for producing intermediates that can serve as substrates for other metabolic processes. Glycolysis takes place through 10 consecutive chemical reactions, each of which is catalysed by a specific enzyme. Although energy transduction by glucose metabolism is the main function of this pathway, involvement in virulence, growth, pathogen-host interactions, immunomodulation and adaptation to environmental conditions are other functions attributed to this metabolic pathway. In humans, where glycolysis occurs mainly in the cytosol, the mislocalization of some glycolytic enzymes in various other subcellular locations, as well as alterations in their expression and regulation, has been associated with the development and progression of various diseases. In this review, we describe the role of glycolytic enzymes in the pathogenesis of diseases of clinical interest. In addition, the potential role of these enzymes as targets for drug development and their potential for use as diagnostic and prognostic markers of some pathologies are also discussed.

Proteome and morphological analysis show unexpected differences between promastigotes of Leishmania amazonensis PH8 and LV79 strains

BACKGROUND

Leishmaniases are diseases caused by Leishmania protozoans that affect around 12 million people. Leishmania promastigotes are transmitted to vertebrates by female phlebotomine flies during their blood meal. Parasites attach to phagocytic cells, are phagocytosed and differentiate into amastigotes. We previously showed that PH8 and LV79 strains of Leishmania amazonensis have different virulence in mice and that their amastigotes differ in their proteomes. In this work, we compare promastigotes' infectivity in macrophages, their proteomes and morphologies.

METHODS/PRINCIPAL FINDINGS

Phagocytosis assays showed that promastigotes adhesion to and phagocytosis by macrophages is higher in PH8 than LV79. To identify proteins that differ between the two strains and that may eventually contribute for these differences we used a label-free proteomic approach to compare promastigote´s membrane-enriched fractions. Proteomic analysis enabled precise discrimination of PH8 and LV79 protein profiles and the identification of several differentially abundant proteins. The proteins more abundant in LV79 promastigotes participate mainly in translation and amino acid and nucleotide metabolism, while the more abundant in PH8 are involved in carbohydrate metabolism, cytoskeleton composition and vesicle/membrane trafficking. Interestingly, although the virulence factor GP63 was more abundant in the less virulent LV79 strain, zymography suggests a higher protease activity in PH8. Enolase, which may be related to virulence, was more abundant in PH8 promastigotes. Unexpectedly, flow cytometry and morphometric analysis indicate higher abundance of metacyclics in LV79.

CONCLUSIONS/SIGNIFICANCE

Proteome comparison of PH8 and LV79 promastigotes generated a list of differential proteins, some of which may be further prospected to affect the infectivity of promastigotes. Although proteomic profile of PH8 includes more proteins characteristic of metacyclics, flow cytometry and morphometric analysis indicate a higher abundance of metacyclics in LV79 cultures. These results shed light to the gaps in our knowledge of metacyclogenesis in L. amazonensis, and to proteins that should be studied in the context of infection by this species.

The History of Anti-Trypanosome Vaccine Development Shows That Highly Immunogenic and Exposed Pathogen-Derived Antigens Are Not Necessarily Good Target Candidates: Enolase and ISG75 as Examples

Salivarian trypanosomes comprise a group of extracellular anthroponotic and zoonotic parasites. The only sustainable method for global control of these infection is through vaccination of livestock animals. Despite multiple reports describing promising laboratory results, no single field-applicable solution has been successful so far. Conventionally, vaccine research focusses mostly on exposed immunogenic antigens, or the structural molecular knowledge of surface exposed invariant immunogens. Unfortunately, extracellular parasites (or parasites with extracellular life stages) have devised efficient defense systems against host antibody attacks, so they can deal with the mammalian humoral immune response. In the case of trypanosomes, it appears that these mechanisms have been perfected, leading to vaccine failure in natural hosts. Here, we provide two examples of potential vaccine candidates that, despite being immunogenic and accessible to the immune system, failed to induce a functionally protective memory response. First, trypanosomal enolase was tested as a vaccine candidate, as it was recently characterized as a highly conserved enzyme that is readily recognized during infection by the host antibody response. Secondly, we re-addressed a vaccine approach towards the Invariant Surface Glycoprotein ISG75, and showed that despite being highly immunogenic, trypanosomes can avoid anti-ISG75 mediated parasitemia control.

Plasminogen-binding proteins as an evasion mechanism of the host's innate immunity in infectious diseases

Pathogens have developed particular strategies to infect and invade their hosts. Amongst these strategies’ figures the modulation of several components of the innate immune system participating in early host defenses, such as the coagulation and complement cascades, as well as the fibrinolytic system. The components of the coagulation cascade and the fibrinolytic system have been proposed to be interfered during host invasion and tissue migration of bacteria, fungi, protozoa, and more recently, helminths. One of the components that has been proposed to facilitate pathogen migration is plasminogen (Plg), a protein found in the host’s plasma, which is activated into plasmin (Plm), a serine protease that degrades fibrin networks and promotes degradation of extracellular matrix (ECM), aiding maintenance of homeostasis. However, pathogens possess Plg-binding proteins that can activate it, therefore taking advantage of the fibrin degradation to facilitate establishment in their hosts. Emergence of Plg-binding proteins appears to have occurred in diverse infectious agents along evolutionary history of host–pathogen relationships. The goal of the present review is to list, summarize, and analyze different examples of Plg-binding proteins used by infectious agents to invade and establish in their hosts. Emphasis was placed on mechanisms used by helminth parasites, particularly taeniid cestodes, where enolase has been identified as a major Plg-binding and activating protein. A new picture is starting to arise about how this glycolytic enzyme could acquire an entirely new role as modulator of the innate immune system in the context of the host–parasite relationship.

Molecular and biochemical characterization of the sunflower (Helianthus annuus L.) cytosolic and plastidial enolases in relation to seed development

In the present study, we describe the molecular and biochemical characterization of sunflower (Helianthus annuus L.) enolase (ENO, EC 4.2.1.11) proteins, which catalyze the formation of phosphoenolpyruvate, the penultimate intermediate in the glycolytic pathway. We cloned and characterized three cDNAs encoding different ENO isoforms from developing sunflower seeds. Studies using fluorescently tagged ENOs confirmed the predicted subcellular localization of ENO isoforms: HaENO1 in the plastid while HaENO2 and HaENO3 were found in the cytosol. The cDNAs were used to express the corresponding 6(His)-tagged proteins in Escherichia coli. The proteins were purified to electrophoretic homogeneity, using immobilized metal ion affinity chromatography, and biochemically characterized. Recombinant HaENO1 and HaENO2, but not HaENO3 were shown to have enolase activity, in agreement with data obtained with the Arabidopsis homolog proteins. Site directed mutagenesis of several critical amino acids was used to attempt to recover enolase activity in recombinant HaENO3, resulting in very small increases that were not additive. A kinetic characterization of the two active isoforms showed that pH had similar effect on their velocity, that they had similar affinity for 2-phosphoglycerate, but that the k_cat/K_m of the plastidial enzyme was higher than that of the cytosolic isoform. Even though HaENO2 was always the most highly expressed transcript, the levels of expression of the three ENO genes were remarkably distinct in all the vegetative and reproductive tissues studied. This indicates that in seeds the conversion of 2-phosphoglycerate to phosphoenolpyruvate takes place through the cytosolic and the plastidial pathways therefore both routes could contribute to the supply of carbon for lipid synthesis. The identity of the main source of carbon during the period of stored products synthesis is discussed.

Insights into the Giardia intestinalis enolase and human plasminogen interaction

Giardia intestinalis is an intestinal parasite that causes diarrhea in humans and animals worldwide. The enolase of G. intestinalis (GiENO) participates in its glycolysis pathway and is abundantly expressed in the parasite cytosol; however, its localization on the surface of trophozoites and cysts has been demonstrated. Enolases from bacteria and parasites can have different functions and are considered moonlighting proteins, for example, as a cell surface plasminogen receptor. In relation to GiENO, no studies have been performed about its possible participation as a plasminogen receptor. In this work, we employed molecular docking and multiscale molecular dynamics (MD) simulations to explore the possible interactions of human plasminogen (HsPLG) with the open and closed GiENO conformations. Our proposed GiENO plasminogen binding site (PLGBs) was identified at Lys266 based on the sequence comparison with bacterial enolase known to act as a plasminogen receptor. Our docking results performed with multiple MD snapshots of the closed GiENO conformation showed that Lys266 preferentially binds to the K5 domain of HsPLG. On the other hand, open GiENO conformations from all-atom and coarse-grained simulations indicated a high preference of the HsPLG K4 domain for lysine residues 186 and 188. Furthermore, we identified a potential N-glycosylation site of GiENO which suggests a possible explanation for the parasite cell surface localization or host mucin oligosaccharide adhesion mechanism. Our study constitutes the first multiscale computational study to explore the plasminogen receptor function of GiENO for its further consideration as a potential therapeutic target for giardiasis treatment.

Probing the efficacy of a heterologous Leishmania/L. Viannia braziliensis recombinant enolase as a candidate vaccine to restrict the development of L. infantum in BALB/c mice

In the present study, the Leishmania braziliensis enolase protein was evaluated as a vaccine candidate against visceral leishmaniasis (VL). The DNA sequence was cloned and the recombinant protein (rEnolase) was evaluated as a vaccine, associated with saponin, as an immune adjuvant. The protective efficacy of the rEnolase plus saponin combination was investigated in BALB/c mice against Leishmania infantum infection. The results revealed that the vaccine induced higher levels of IFN-γ, IL-12, and GM-CSF when a capture ELISA and flow cytometry were performed, as well as an antileishmanial nitrite production after using in vitro stimulation with rEnolase and an antigenic Leishmania preparation. The vaccinated animals, when compared to the control groups, showed a lower parasite burden in the liver, spleen, bone marrow, and paws' draining lymph nodes when both a limiting dilution technique and RT-PCR assay were performed. In addition, these mice showed low levels of antileishmanial IL-4, IL-10, and anti-Leishmania IgG1 isotype antibodies. Partial protection was associated with IFN-γ production, which was mainly mediated by CD4⁺ T cells. In conclusion, the present study's data showed that the L. braziliensis enolase protein could be considered a vaccine candidate that offers heterologous protection against VL.

Subcellular localization of glycolytic enzymes and characterization of intermediary metabolism of Trypanosoma rangeli

Trypanosoma rangeli is a hemoflagellate protist that infects wild and domestic mammals as well as humans in Central and South America. Although this parasite is not pathogenic for human, it is being studied because it shares with Trypanosoma cruzi, the etiological agent of Chagas' disease, biological characteristics, geographic distribution, vectors and vertebrate hosts. Several metabolic studies have been performed with T. cruzi epimastigotes, however little is known about the metabolism of T. rangeli. In this work we present the subcellular distribution of the T. rangeli enzymes responsible for the conversion of glucose to pyruvate, as determined by epifluorescense immunomicroscopy and subcellular fractionation involving either selective membrane permeabilization with digitonin or differential and isopycnic centrifugation. We found that in T. rangeli epimastigotes the first six enzymes of the glycolytic pathway, involved in the conversion of glucose to 1,3-bisphosphoglycerate are located within glycosomes, while the last four steps occur in the cytosol. In contrast with T. cruzi, where three isoenzymes (one cytosolic and two glycosomal) of phosphoglycerate kinase are expressed simultaneously, only one enzyme with this activity is detected in T. rangeli epimastigotes, in the cytosol. Consistent with this latter result, we found enzymes involved in auxiliary pathways to glycolysis needed to maintain adenine nucleotide and redox balances within glycosomes such as phosphoenolpyruvate carboxykinase, malate dehydrogenase, fumarate reductase, pyruvate phosphate dikinase and glycerol-3-phosphate dehydrogenase. Glucokinase, galactokinase and the first enzyme of the pentose-phosphate pathway, glucose-6-phosphate dehydrogenase, were also located inside glycosomes. Furthermore, we demonstrate that T. rangeli epimastigotes growing in LIT medium only consume glucose and do not excrete ammonium; moreover, they are unable to survive in partially-depleted glucose medium. The velocity of glucose consumption is about 40% higher than that of procyclic Trypanosoma brucei, and four times faster than by T. cruzi epimastigotes under the same culture conditions.

Immunolocation and enzyme activity analysis of Cryptosporidium parvum enolase

Background

Enolase is an essential multifunctional glycolytic enzyme that is involved in many biological processes of apicomplexan protozoa, such as adhesion and invasion. However, the characteristics of enolase in Cryptosporidium parvum, including the location on the oocyst and the enzyme activity, remain unclear.

Methods

The C. parvum enolase gene (cpeno) was amplified by RT-PCR and sequenced. The deduced amino acid sequence was analysed by bioinformatics software. The gene was expressed in Escherichia coli BL21 (DE3) and purified recombinant protein was used for enzyme activity analysis, binding experiments and antibody preparation. The localisation of enolase on oocysts was examined via immunofluorescence techniques.

Results

A 1,350 bp DNA sequence was amplified from cDNA taken from C. parvum oocysts. The deduced amino acids sequence of C. parvum enolase (CpEno) had 82.1% homology with Cryptosporidium muris enolase, and 54.7–68.0% homology with others selected species. Western blot analysis indicated that recombinant C. parvum enolase (rCpEno) could be recognised by C. parvum-infected cattle sera. Immunolocalization testing showed that CpEno was found to locate mainly on the surface of oocysts. The enzyme activity was 33.5 U/mg, and the Michaelis constant (K_m) was 0.571 mM/l. Kinetic measurements revealed that the most suitable pH value was 7.0–7.5, and there were only minor effects on the activity of rCpEno with a change in the reaction temperature. The enzyme activity decreased when the Ca²⁺, K⁺, Mg²⁺ and Na⁺ concentrations of the reaction solution increased. The binding assays demonstrated that rCpEno could bind to human plasminogen.

Conclusion

This study is the first report of immunolocation, binding activity and enzyme characteristics of CpEno. The results of this study suggest that the surface-associated CpEno not only functions as a glycolytic enzyme but may also participate in attachment and invasion process of the parasite.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-017-2200-y) contains supplementary material, which is available to authorized users.

Integrating genomics and proteomics permits identification of immunodominant antigens associated with drug resistance in human visceral leishmaniasis in India

Resistance of human pathogens like Leishmania to drugs is a growing concern where the multidrug-resistant phenotype renders chemotherapy ineffective. The acquired resistance of Leishmania to antimony has promoted intense research on the mechanisms involved but the question has not been resolved yet. In this study we have explored host-pathogen- drug interactions leading to identification of pharmacological determinants of host macrophages that resist the sodium antimony gluconate (SAG) mediated intracellular parasite killing. mRNA profiling of mammalian host stage amastigotes of sodium antimony gluconate (SAG) 'sensitive' and 'resistant' parasite lines was carried out using Affymetrix GeneChip^® Human Genome U133 Plus 2.0 Array. Patient sera was used to identify immunogenic proteins by two-dimensional gel analysis (2DE) and mass spectrometric analysis (LC-MS/MS). Immunofluorescence microscopy confirmed the identities on 'sensitive' and 'resistant' parasite lines. A total of nine immunogenic proteins whose intensities changed significantly and consistently in multiple experiments were detected, suggesting that a cohort of proteins are altered in expression levels in the 'resistant' parasites. Global expression profiling using microarrays revealed this regulation was not reflected by changes in the levels of the cognate mRNAs. Following identification of proteins by mass spectrometry, one such regulated protein, enolase, was chosen for more detailed analysis. Immunofluorescence microscopy employing antisera against this enzyme confirmed that its level was differentially regulated in the 'resistant' isolate. We show that high serum level of immunoreactive protein is associated with 'resistant' phenotype. Differentially expressed proteins with immunomodulatory activities were found to be associated with the 'resistant phenotype'.

Identification and characterization of an immunogenic antigen, enolase 2, among excretory/secretory antigens (ESA) of Toxoplasma gondii

An immunogenic protein, enolase 2, was identified among the secreted excretory/secretory antigens (ESAs) from Toxoplasma gondii strain RH using immunoproteomics based on matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Enolase 2 was cloned, sequenced, and heterologously expressed. BLAST analysis revealed 75-96% similarity with enolases from other parasites. Immunoblotting demonstrated good immunoreactivity of recombinant T. gondii enolase (Tg-enolase 2) to T. gondii-infected animal serum. Purified Tg-enolase 2 was found to catalyze dehydration of 2-phospho-d-glycerate to phosphoenolpyruvate. In vitro studies revealed maximal activity at pH 7.5 and 37 °C, and activity was inhibited by K(+), Ni(2+), Al(3+), Na(+), Cu(2+) and Cr(3+). A monoclonal antibody against Tg-enolase 2 was prepared, 1D6, with the isotype IgG2a/κ. Western blotting revealed that 1D6 reacts with Tg-enolase 2 and native enolase 2, present among T. gondii ESAs. The indirect immunofluorescence assays showed that enolase 2 could be specifically detected on the growing T. gondii tachyzoites. Immunoelectron microscopy revealed the surface and intracellular locations of enolase 2 on T. gondii cells. In conclusion, our results clearly show that the enzymatic activity of T. gondii enolase 2 is ion dependent and that it could be influenced by environmental factors. We also provide evidence that enolase 2 is an important immunogenic protein of ESAs from T. gondii and that it is a surface-exposed protein with strong antigenicity and immunogenicity. Our findings indicate that enolase 2 could play important roles in metabolism, immunogenicity and pathogenicity and that it may serve as a novel drug target and candidate vaccine against T. gondii infection.

Unique behavior of Trypanosoma cruzi mevalonate kinase: A conserved glycosomal enzyme involved in host cell invasion and signaling

Mevalonate kinase (MVK) is an essential enzyme acting in early steps of sterol isoprenoids biosynthesis, such as cholesterol in humans or ergosterol in trypanosomatids. MVK is conserved from bacteria to mammals, and localizes to glycosomes in trypanosomatids. During the course of T. cruzi MVK characterization, we found that, in addition to glycosomes, this enzyme may be secreted and modulate cell invasion. To evaluate the role of TcMVK in parasite-host cell interactions, TcMVK recombinant protein was produced and anti-TcMVK antibodies were raised in mice. TcMVK protein was detected in the supernatant of cultures of metacyclic trypomastigotes (MTs) and extracellular amastigotes (EAs) by Western blot analysis, confirming its secretion into extracellular medium. Recombinant TcMVK bound in a non-saturable dose-dependent manner to HeLa cells and positively modulated internalization of T. cruzi EAs but inhibited invasion by MTs. In HeLa cells, TcMVK induced phosphorylation of MAPK pathway components and proteins related to actin cytoskeleton modifications. We hypothesized that TcMVK is a bifunctional enzyme that in addition to playing a classical role in isoprenoid synthesis in glycosomes, it is secreted and may modulate host cell signaling required for T. cruzi invasion.

Trypanosoma evansi contains two auxiliary enzymes of glycolytic metabolism: Phosphoenolpyruvate carboxykinase and pyruvate phosphate dikinase

Trypanosoma evansi is a monomorphic protist that can infect horses and other animal species of economic importance for man. Like the bloodstream form of the closely related species Trypanosoma brucei, T. evansi depends exclusively on glycolysis for its free-energy generation. In T. evansi as in other kinetoplastid organisms, the enzymes of the major part of the glycolytic pathway are present within organelles called glycosomes, which are authentic but specialized peroxisomes. Since T. evansi does not undergo stage-dependent differentiations, it occurs only as bloodstream forms, it has been assumed that the metabolic pattern of this parasite is identical to that of the bloodstream form of T. brucei. However, we report here the presence of two additional enzymes, phosphoenolpyruvate carboxykinase and PPi-dependent pyruvate phosphate dikinase in T. evansi glycosomes. Their colocalization with glycolytic enzymes within the glycosomes of this parasite has not been reported before. Both enzymes can make use of PEP for contributing to the production of ATP within the organelles. The activity of these enzymes in T. evansi glycosomes drastically changes the model assumed for the oxidation of glucose by this parasite.

Proteins Selected in Leishmania (Viannia) braziliensis by an Immunoproteomic Approach with Potential Serodiagnosis Applications for Tegumentary Leishmaniasis

The serodiagnosis of human tegumentary leishmaniasis (TL) presents some problems, such as the low level of antileishmanial antibodies found in most of the patients, as well as the cross-reactivity in subjects infected by other trypanosomatids. In the present study, an immunoproteomic approach was performed aimed at identification of antigens in total extracts of stationary-phase promastigote and amastigote-like forms of Leishmania (Viannia) braziliensis using sera from TL patients. With the purpose of reducing the cross-reactivity of the identified proteins, spots recognized by sera from TL patients, as well as those recognized by antibodies present in sera from noninfected patients living in areas where TL is endemic and sera from Chagas disease patients, were discarded. Two Leishmania hypothetical proteins and 18 proteins with known functions were identified as antigenic. The study was extended with some of them to validate the results of the immunoscreening. The coding regions of five of the characterized antigens (enolase, tryparedoxin peroxidase, eukaryotic initiation factor 5a, β-tubulin, and one of the hypothetical proteins) were cloned in a prokaryotic expression vector, and the corresponding recombinant proteins were purified and evaluated for the serodiagnosis of TL. The antigens presented sensitivity and specificity values ranging from 95.4 to 100% and 82.5 to 100%, respectively. As a comparative antigen, a preparation of Leishmania extract showed sensitivity and specificity values of 65.1 and 57.5%, respectively. The present study has enabled the identification of proteins able to be employed for the serodiagnosis of TL.

Seahorse-derived peptide suppresses invasive migration of HT1080 fibrosarcoma cells by competing with intracellular α-enolase for plasminogen binding and inhibiting uPA-mediated activation of plasminogen

α-Enolase is a glycolytic enzyme and a surface receptor for plasminogen. α-Enolase-bound plasminogen promotes tumor cell invasion and cancer metastasis by activating plasmin and consequently degrading the extracellular matrix degradation. Therefore, α-enolase and plasminogen are novel targets for cancer therapy. We found that the amino acid sequence of a peptide purified from enzymatic hydrolysates of seahorse has striking similarities to that of α-enolase. In this study, we report that this peptide competes with cellular α-enolase for plasminogen binding and suppresses urokinase plasminogen activator (uPA)-mediated activation of plasminogen, which results in decreased invasive migration of HT1080 fibrosarcoma cells. In addition, the peptide treatment decreased the expression levels of uPA compared to that of untreated controls. These results provide new insight into the mechanism by which the seahorse-derived peptide suppresses invasive properties of human cancer cells. Our findings suggest that this peptide could emerge as a potential therapeutic agent for cancer. [BMB Reports 2014; 47(12): 691-696]

Comparative immunoprophylactic efficacy of Haemonchus contortus recombinant enolase (rHcENO) and Con A purified native glycoproteins in sheep

Haemonchus contortus is the most economically important blood feeding nematode parasite of sheep and goats all over the world. Enolase in helminth parasites is a multi-functional enzyme which involves in glycolysis and host tissue invasion. In this study, the recombinant H. contortus enolase (rHcENO) was evaluated for its immunoprophylactic efficacy in sheep along with Con A purified native glycoproteins in a vaccine challenge trial. Group I and Group II experimental sheep were immunized thrice with rHcENO and Con A purified native glycoproteins along with Montanide ISA 61 VG adjuvant. The animals were challenged with 5000 L3 stage active H. contortus larvae after 21 days of third immunization. A significant increase in the IgG titre was observed in rHcENO and Con A purified native glycoproteins immunized animals as compared to the control animals. Immunoprotective efficacy of Con A purified native glycoproteins was comparatively higher than rHcENO antigen.

Moonlighting proteins as virulence factors of pathogenic fungi, parasitic protozoa and multicellular parasites

The delicate balance between eukaryotic pathogens and their human hosts during the initiation and development of infection is a complex process involving many diverse interactions. Different infectious agents, including pathogenic fungi, parasitic protozoa and multicellular parasites, directly interact through their cell surface with epithelial or endothelial cells of the human host as well as various proteinaceous host ligands such as extracellular matrix or plasma proteins. Eukaryotic pathogens possess a number of virulence factors but a relatively recently recognized and particularly interesting group of factors capable of enhancing virulence is the set of so-called 'moonlighting proteins'. This term was coined for a relatively large collection of housekeeping enzymes lacking special targeting motifs that would determine their extracellular localization, but that are often present at the cell surface of pathogen. Several such enzymes with key metabolic functions in glycolysis, the pentose phosphate cycle or other fundamental intracellular processes perform entirely new, non-catalytic roles often associated with adhesion to host ligands. Our current study summarizes some of the current knowledge of interesting moonlighting proteins which play putative or confirmed roles as virulence factors in pathogenic fungi, parasitic protozoa and multicellular parasites.

Extracellular functions of glycolytic enzymes of parasites: unpredicted use of ancient proteins

In addition of their usual intracellular localization where they are involved in catalyzing reactions of carbohydrate and energy metabolism by glycolysis, multiple studies have shown that glycolytic enzymes of many organisms, but notably pathogens, can also be present extracellularly. In the case of parasitic protists and helminths, they can be found either secreted or attached to the surface of the parasites. At these extracellular localizations, these enzymes have been shown to perform additional, very different so-called "moonlighting" functions, such as acting as ligands for a variety of components of the host. Due to this recognition, different extracellular glycolytic enzymes participate in various important parasite-host interactions such as adherence and invasion of parasites, modulation of the host's immune and haemostatic systems, promotion of angiogenesis, and acquisition of specific nutrients by the parasites. Accordingly, extracellular glycolytic enzymes are important for the invasion of the parasites and their establishment in the host, and in determining their virulence.

Characterization of glycolytic enzymes--rAldolase and rEnolase of Leishmania donovani, identified as Th1 stimulatory proteins, for their immunogenicity and immunoprophylactic efficacies against experimental visceral leishmaniasis

Th1 immune responses play an important role in controlling Visceral Leishmaniasis (VL) hence, Leishmania proteins stimulating T-cell responses in host, are thought to be good vaccine targets. Search of such antigens eliciting cellular responses in Peripheral blood mononuclear cells (PBMCs) from cured/exposed/Leishmania patients and hamsters led to the identification of two enzymes of glycolytic pathway in the soluble lysate of a clinical isolate of Leishmania donovani--Enolase (LdEno) and aldolase (LdAld) as potential Th1 stimulatory proteins. The present study deals with the molecular and immunological characterizations of LdEno and LdAld. The successfully cloned and purified recombinant proteins displayed strong ability to proliferate lymphocytes of cured hamsters' along with significant nitric-oxide production and generation of Th1-type cytokines (IFN-γ and IL-12) from stimulated PBMCs of cured/endemic VL patients. Assessment of their prophylactic potentials revealed ∼ 90% decrease in parasitic burden in rLdEno vaccinated hamsters against Leishmania challenge, strongly supported by an increase in mRNA expression levels of iNOS, IFN-γ, TNF-α and IL-12 transcripts along with extreme down-regulation of TGF-β, IL-4 and IL-10. However, animals vaccinated with rLdAld showed comparatively lesser prophylactic efficacy (∼ 65%) with inferior immunological response. Further, with a possible implication in vaccine design against VL, identification of potential T-cell epitopes of both the proteins was done using computational approach. Additionally, in-silico 3-D modelling of the proteins was done in order to explore the possibility of exploiting them as potential drug targets. The comparative molecular and immunological characterizations strongly suggest rLdEno as potential vaccine candidate against VL and supports the notion of its being effective T-cell stimulatory protein.

A Trypanosoma brucei kinesin heavy chain promotes parasite growth by triggering host arginase activity

BACKGROUND

In order to promote infection, the blood-borne parasite Trypanosoma brucei releases factors that upregulate arginase expression and activity in myeloid cells.

METHODOLOGY/PRINCIPAL FINDINGS

By screening a cDNA library of T. brucei with an antibody neutralizing the arginase-inducing activity of parasite released factors, we identified a Kinesin Heavy Chain isoform, termed TbKHC1, as responsible for this effect. Following interaction with mouse myeloid cells, natural or recombinant TbKHC1 triggered SIGN-R1 receptor-dependent induction of IL-10 production, resulting in arginase-1 activation concomitant with reduction of nitric oxide (NO) synthase activity. This TbKHC1 activity was IL-4Rα-independent and did not mirror M2 activation of myeloid cells. As compared to wild-type T. brucei, infection by TbKHC1 KO parasites was characterized by strongly reduced parasitaemia and prolonged host survival time. By treating infected mice with ornithine or with NO synthase inhibitor, we observed that during the first wave of parasitaemia the parasite growth-promoting effect of TbKHC1-mediated arginase activation resulted more from increased polyamine production than from reduction of NO synthesis. In late stage infection, TbKHC1-mediated reduction of NO synthesis appeared to contribute to liver damage linked to shortening of host survival time.

CONCLUSION

A kinesin heavy chain released by T. brucei induces IL-10 and arginase-1 through SIGN-R1 signaling in myeloid cells, which promotes early trypanosome growth and favors parasite settlement in the host. Moreover, in the late stage of infection, the inhibition of NO synthesis by TbKHC1 contributes to liver pathogenicity.

Plasminogen binding proteins in secreted membrane vesicles of Leishmania mexicana

Membrane vesicles secreted by Leishmania mexicana were collected and analyzed. These vesicles can bind plasminogen and were shown to contain enolase, previously identified as a plasminogen-binding protein. In addition, another plasminogen-binding protein was identified, the small myristoylated protein, SMP-1. Recombinant SMP-1 was able to bind plasminogen in a lysine-dependent manner with a K(d) value of 0.24 μM. The C-terminal lysine seems to be responsible for this binding, since this recognition decreases upon carboxypeptidase B treatment. This protein was present within the secreted membrane vesicles as demonstrated by its protection from trypsin digestion in the absence of Triton X-100. Plasminogen-binding proteins in the secreted vesicles may be involved in parasite invasion in the mammalian host.

Steinernema glaseri surface enolase: molecular cloning, biological characterization, and role in host immune suppression

Entomopathogenic nematodes are widely used as biological control agents that can suppress or evade the host immune defense upon entry into insects. The surface coat of Steinernema glaseri has been shown to play important roles in defeating the host immune system. In this work, a protein fraction with antiphagocytic activity was separated by electro-elution and further analyzed by two-dimensional electrophoresis (2-DE). LC-MS/MS analysis of one protein spot from a 2-DE gel gave five peptides that were highly similar to enolases of many organisms. A 1311 bp cDNA was cloned that encodes a 47 kDa protein with high sequence identity to enolases from different species of nematodes. The deduced protein, Sg-ENOL, was expressed in Escherichia coli, and its glycolytic activity was demonstrated by the conversion of 2-phospho-d-glycerate to phosphoenolpyruvate. Recombinant Sg-ENOL significantly reduced the LT(50)s of Xenorhabdus poinarii and Metarhizium anisopliae when co-injected into Galleria mellonella and Locusta migratoria manilensis Meyen, respectively. Using immuno-gold transmission electron microscopy, native Sg-ENOL was confirmed to be localized to both the nematode cuticle and the surface coat. In vitro, secretion of Sg-ENOL was inducible rather than constitutive. In vivo, Sg-ENOL was detected in the host hemolymph after infection of G. mellonella with S. glaseri, indicating that Sg-ENOL was secreted into the insect hemocoel and was involved in infection. This is the first report of the cloning and characterization of a surface coat protein in an entomopathogenic nematode. Our findings provide clear evidence for an important role for a cell surface enolase in S. glaseri infection and host immune suppression.

Surface-expressed enolase contributes to the adhesion of Paracoccidioides brasiliensis to host cells

Paracoccidioidomycosis is a systemic mycosis caused by the dimorphic fungus Paracoccidioides brasiliensis. Understanding the interactions between P. brasiliensis and the host tissue depends on the study of the different steps of the process of colonization, especially adhesion, in which the pathogen recognizes ligands on the surface of host cells. This study aimed to verify the role of enolase in the host cell-fungus interaction and the ability of enolase to bind to extracellular matrix components, to determine its subcellular localization, and to study the P. brasiliensis enolase amino acid sequence. The data revealed that fibronectin is the major ligand of enolase. Evaluation of the location of enolase at an ultrastructural level revealed that it is distributed in various cellular compartments, but at a high level in the cell wall. The analysis of the amino acid sequence revealed an internal plasminogen-binding motif ((254)FYKADEKKY(262)), which is conserved in most organisms and described as an important interaction site of the enolase with the host cell surface. This suggests that enolase performs additional functions related to the glycolytic pathway and also plays a role of adhesion in P. brasiliensis. Therefore, this study increases the knowledge about the characteristics of enolase and its influence on the binding process of P. brasiliensis.

Surface-expressed enolases of Plasmodium and other pathogens

Enolase is the eighth enzyme in the glycolytic pathway, a reaction that generates ATP from phosphoenol pyruvate in cytosolic compartments. Enolase is essential, especially for organisms devoid of the Krebs cycle that depend solely on glycolysis for energy. Interestingly, enolase appears to serve a separate function in some organisms, in that it is also exported to the cell surface via a poorly understood mechanism. In these organisms, surface enolase assists in the invasion of their host cells by binding plasminogen, an abundant plasma protease precursor. Binding is mediated by the interaction between a lysine motif of enolase with Kringle domains of plasminogen. The bound plasminogen is then cleaved by specific proteases to generate active plasmin. Plasmin is a potent serine protease that is thought to function in the degradation of the extracellular matrix surrounding the targeted host cell, thereby facilitating pathogen invasion. Recent work revealed that the malaria parasite Plasmodium also expresses surface enolase, and that this feature may be essential for completion of its life cycle. The therapeutic potential of targeting surface enolases of pathogens is discussed.

Plasmodium ookinetes coopt mammalian plasminogen to invade the mosquito midgut

Ookinete invasion of the mosquito midgut is an essential step for the development of the malaria parasite in the mosquito. Invasion involves recognition between a presumed mosquito midgut receptor and an ookinete ligand. Here, we show that enolase lines the ookinete surface. An antienolase antibody inhibits oocyst development of both Plasmodium berghei and Plasmodium falciparum, suggesting that enolase may act as an invasion ligand. Importantly, we demonstrate that surface enolase captures plasminogen from the mammalian blood meal via its lysine motif (DKSLVK) and that this interaction is essential for midgut invasion, because plasminogen depletion leads to a strong inhibition of oocyst formation. Although addition of recombinant WT plasminogen to depleted serum rescues oocyst formation, recombinant inactive plasminogen does not, thus emphasizing the importance of plasmin proteolytic activity for ookinete invasion. The results support the hypothesis that enolase on the surface of Plasmodium ookinetes plays a dual role in midgut invasion: by acting as a ligand that interacts with the midgut epithelium and, further, by capturing plasminogen, whose conversion to active plasmin promotes the invasion process.

Enolase: a key player in the metabolism and a probable virulence factor of trypanosomatid parasites-perspectives for its use as a therapeutic target

Glycolysis and glyconeogenesis play crucial roles in the ATP supply and synthesis of glycoconjugates, important for the viability and virulence, respectively, of the human-pathogenic stages of Trypanosoma brucei, Trypanosoma cruzi, and Leishmania spp. These pathways are, therefore, candidate targets for antiparasite drugs. The glycolytic/gluconeogenic enzyme enolase is generally highly conserved, with similar overall fold and identical catalytic residues in all organisms. Nonetheless, potentially important differences exist between the trypanosomatid and host enzymes, with three unique, reactive residues close to the active site of the former that might be exploited for the development of new drugs. In addition, enolase is found both in the secretome and in association with the surface of Leishmania spp. where it probably functions as plasminogen receptor, playing a role in the parasite's invasiveness and virulence, a function possibly also present in the other trypanosomatids. This location and possible function of enolase offer additional perspectives for both drug discovery and vaccination.

Clonorchis sinensis enolase: identification and biochemical characterization of a glycolytic enzyme from excretory/secretory products

Enolase plays a key role in energy metabolism and development of most organisms. We isolated a gene encoding enolase from Clonorchis sinensis (C. sinensis) adult cDNA library and expressed the recombinant protein in Escherichia coli. C. sinensis enolase (Csenolase) was identified as both an excretory/secretory product and a tegumental component of C. sinensis by western blot analysis. The transcriptional level of Csenolase was examined at adult worm, metacercaria, cercaria and egg of C. sinensis, and results showed that Csenolase is transcribed at the four life stages of C. sinensis while showing a significant higher expression level at the stage of adult worm. Immunohistochemical localization indicated that Csenolase was specifically deposited on the tegument of adult worm and cyst wall of metacercaria. Ligand blot assay revealed a specific characteristic of dose-dependent plasminogen-binding activity of Csenolase and kinetic parameters were explored using 2-phospho-D-glycerate (2-PGA) as the primary substrate by monitoring the conversion of nicotinamide-adenine dinucleotide (NADH) into nicotinamide adenine dinucleotide (NAD). In addition, Csenolase exhibited active enzyme activity in catalytic reactions while the anti-Csenolase serum inhibited the enzyme activity. In vitro incubation experiments revealed that Csenolase might play key roles in the growth of the parasites. In conclusion, Csenolase is an important glycolytic enzyme required for the development of C. sinensis, and may be a potential vaccine candidate and drug target against C. sinensis infection.

Cloning, expression and characterization of NAD+-dependent glyceraldehyde-3-phosphate dehydrogenase of adult Haemonchus contortus†

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) regulates a wide range of biological processes, including pathogen evasion. In the present research, the GAPDH gene of Haemonchus contortus (HcGAPDH) was cloned and characterized. Specific primers for the rapid amplification of cDNA ends (RACE) were designed based on the expressed sequence tag (EST, AW670737) to amplify the 3′ and 5′ ends of HcGAPDH. The full length of cDNA from this gene was obtained by overlapping the sequences of 3′ and 5′ extremities and amplification by reverse transcription polymerase chain reaction (RT-PCR). The biochemical activities of the recombinant protein HcGAPDH, which was expressed in prokaryotic cells and purified by affinity chromatography, were analysed by assays of enzymatic activity, thermal stability and pH. The results showed that the cloned full-length cDNA comprised 1303 bp and encoded a peptide with 341 amino acid residues which showed sequence similarity to several known GAPDHs. The biochemical assay showed that the protein encoded by the HcGAPDH exhibited enzymatic activity with NAD+ as a cofactor. HcGAPDH was stable between pH 5 and 9 and maintained activity at high temperatures of up to 75°C. The natural GAPDH of Haemonchus contortus detected by immunoblot assay was approximately 38 kDa in size, and the recombinant HcGAPDH was recognized strongly by serum from naturally infected goats.

The oligopeptidase B of Leishmania regulates parasite enolase and immune evasion

Proteases are a ubiquitous group of enzymes that play key roles in the life cycle of parasites, in the host-parasite relationship, and in the pathogenesis of parasitic diseases. Furthermore, proteases are targets for the development of new anti-parasitic therapy. Protozoan parasites like Leishmania predominantly express Clan CA cysteine proteases for key life cycle functions. It was therefore unexpected to find a high level of serine protease activity expressed by Leishmania donovani. Purification of this activity followed by mass spectrometry identified oligopeptidase B (OPB; Clan SC, family S9A) as the responsible enzyme. This was confirmed by gene knock-out of OPB, which resulted in the disappearance of the detected serine protease activity of Leishmania extracts. To delineate the specific role of OPB in parasite physiology, proteomic analysis was carried out on OPB(-/-) versus wild type parasites. Four protein species were significantly elevated in OPB(-/-) parasites, and all four were identified by mass spectrometry as enolase. This increased enolase was enzymatically inactive and associated with the parasite membrane. Aside from its classic role in carbohydrate metabolism, enolase was recently found to localize to membranes, where it binds host plasminogen and functions as a virulence factor for several pathogens. As expected, there was a striking alteration in macrophage responses to Leishmania when OPB was deleted. Whereas wild type parasites elicited little, if any, response from infected macrophages, OPB(-/-) parasites induced a massive up-regulation in gene transcription. Additionally, these OPB(-/-) parasites displayed decreased virulence in the murine footpad infection model.

Moonlighting enzymes in parasitic protozoa

Enzymes moonlight in a non-enzymatic capacity in a diverse variety of cellular processes. The discovery of these non-enzymatic functions is generally unexpected, and moonlighting enzymes are known in both prokaryotes and eukaryotes. Importantly, this unexpected multi-functionality indicates that caution might be needed on some occasions in interpreting phenotypes that result from the deletion or gene-silencing of some enzymes, including some of the best known enzymes from classic intermediary metabolism. Here, we provide an overview of enzyme moonlighting in parasitic protists. Unequivocal and putative examples of moonlighting are discussed, together with the possibility that the unusual biological characteristics of some parasites either limit opportunities for moonlighting to arise or perhaps contribute to the evolution of novel proteins with clear metabolic ancestry.

Reverse vaccinology approach identify an Echinococcus granulosus tegumental membrane protein enolase as vaccine candidate

Applying reverse vaccinology strategy, we employed a sequence encoding an enolase from Taenia asiatica to search its homolog in the expression sequence tag (EST) database of Echinococcus granulosus and found two EST sequences (Access number: CN653186 and CN649593) of a clone Eg_PSGRS_13B09 from E. granulosus protoscolex full-length cDNA library, which are responding for the 5' and 3' partial cds of E. granulosus enolase, respectively. Primers are designed according to the 5' end and 3'end of the putative encoding sequence to amplify the genomic DNA of E. granulosus strain isolated from sheep in Qinghai province of China by polymerase chain reaction (PCR). A sole product of 1,449 bp in length was obtained, which contains two little introns of 78 bp and 69 bp, respectively. The introns were excised by unsymmetrical PCR with combined flank sequences of introns as primers. The structural, functional, and immunological characteristics of putative amino acid sequence were predicted by bioinformatics analysis. The complete coding sequence was predicted to encode 433 residues and contain a transmembrane region aa(104-124), with the N terminus outside and C terminus inside. The inside part is quite the functional domain. SWISS-MODEL modulated its 3D structure as a barrel which constitutes of alternatively arranged alpha helix-beta sheet, with the key sites such as substrate binding region, active sites, Mg(2+)-binding sites closely located at the center. The protein contains a potential nuclear localization sequence aa(190-199) and several linear B cell epitopes and CTL T cell epitopes, of which the outside epitope aa(49-57) and inside epitope aa(228-236) are facultative T cell and B cell epitope, and the linear B cell epitope aa(206-213) contains the active center site Glu(210), suggesting the putative protein is a potential membrane with strong immunogenicity. The complete cds was expressed in Escherichia coli, and the recombinant protein can be recognized by the serum from patient infected with E. granulosus. Reverse vaccinology process identified E. granulosus tegumental membrane protein enolase as vaccine candidate.

Proteomic examination of Leishmania chagasi plasma membrane proteins: Contrast between avirulent and virulent (metacyclic) parasite forms

PURPOSE

About two million new cases of leishmaniasis with 50 000 associated deaths occur worldwide each year. Promastigotes of the causative Leishmania spp. develop from the procyclic stage to the highly virulent metacyclic stage within the sand fly vector. We hypothesized that proteins important for promastigote virulence might be uniquely represented in the plasma membrane of metacyclic, but not procyclic, promastigotes.

EXPERIMENTAL DESIGN

Procyclic (logarithmic) promastigotes and purified metacyclic promastigotes from stationary phase cultures of Leishmania chagasi were used to prepare membrane preparations either by surface biotinylation-streptavidin affinity separation or by octyl glucoside detergent extraction.

RESULTS

These membrane fractions were enriched over 130- and 250-fold, respectively, as estimated by Western blotting for the plasma membrane's major surface protease. Hundreds or dozens of proteins were identified by LC-MS/MS in the surface biotinylation or detergent extraction, respectively. Confocal microscopy suggested the difference between the lists was due to the fact that proteins localized both on the surface membrane and within the flagellar pocket were accessible to surface biotinylation, whereas only proteins on the membrane were obtained by detergent extraction. Using detergent extraction, we found different proteins were present in membranes of the procyclic stage compared to metacyclic stage promastigotes. Several dozen were stage specific.

CONCLUSIONS AND CLINICAL RELEVANCE

These data provide a foundation for identifying virulence factors in the plasma membranes of Leishmania spp. promastigotes during metacyclogenesis.

Aphidius ervi teratocytes release an extracellular enolase

We report the cloning of a gene and the characterization of the encoded protein, which is released by the teratocytes of the parasitoid Aphidius ervi in the haemocoel of the host aphid Acyrthosiphon pisum. The studied protein was identified by LC-MS/MS, and the gathered information used for isolating the full length cDNA. The corresponding gene was made of 3 exons and 2 introns, and was highly expressed in the adult wasps and in parasitized hosts. The translation product, which was named Ae-ENO, showed a very high level of sequence identity with insect enolases. In vivo immunodetection experiments evidenced Ae-ENO localization in round spots, present in the teratocytes and released in the host haemocoel. Moreover, strong immunoreactivity was detected on the surface of A. ervi larvae and of host embryos. Ae-ENO expressed in insect cells was not secreted in the medium, indicating the occurrence in the teratocytes of an unknown pathway for Ae-ENO release. The recombinant protein produced in bacteria under native conditions was a dimer, with evident enolase activity (K(m) = 0.086 +/- 0.017 mM). Enolase is a well known enzyme in cell metabolism, which, however, is associated with a multifunctional role in disease, when present in the extracellular environment, on the surface of prokaryotic and eukaryotic cells. In these cases, the enolase mediates the activation of enzymes involved in the invasion of tissues by pathogens and tumour cells, and in the evasion of host immune response. The possible role played by Ae-ENO in the host regulation process is discussed in the light of this information.

Sarcocystis neurona: molecular characterization of enolase domain I region and a comparison to other protozoa

Sarcocystis neurona causes protozoal myeloencephalitis and has the ability to infect a wide host range in contrast to other Sarcocystis species. In the current study, five S. neurona isolates from a variety of sources, three Sarcocystis falcatula, one Sarcocystis dasypi/S. neurona-like isolate, and one Besnoitia darlingi isolate were used to compare the enolase 2 gene segment containing the domain I region to previously sequenced enolase genes from Neospora caninum, Neospora hughesi, Toxoplasma gondii, Plasmodium falciparum, and Trypanosoma cruzi; enolase 2 segment containing domain I region is highly conserved amongst these parasites of veterinary and medical importance. Immunohistochemistry results indicates reactivity of T. gondii enolase 1 and 2 antibodies to S. neurona merozoites and metrocytes, but no reactivity of anti-enolase 1 to the S. neurona bradyzoite stage despite reactivity to T. gondii bradyzoites, suggesting expression differences between organisms.

Characteristics of plasminogen binding to Trypanosoma cruzi epimastigotes

The binding constants of the interaction between plasminogen and Trypanosoma cruzi epimastigotes were determined. An indirect method in which the bound plasminogen is detached from the cell by epsilon-aminocaproic acid and a direct method through biotinylated plasminogen were used. The analyses revealed a dissociation constant (Kd) from 0.4 to 1.2microM, these values being compatible with recognition in vivo. Moreover, epimastigotes from the gut of Rhodnius prolixus were able to bind plasminogen from the blood meal. Fragments derived from elastase digestion of plasminogen were tested for their ability to bind T. cruzi cells. The fragment with highest ability to interact with the parasite was miniplasminogen that bound in a concentration-dependent and saturable manner with a Kd similar to that for plasminogen. This binding was inhibited by epsilon-aminocaproic acid indicating that the lysine-binding site of kringle 5 may be responsible for the interaction of plasminogen with T. cruzi.

Structural flexibility in Trypanosoma brucei enolase revealed by X-ray crystallography and molecular dynamics

Enolase is a validated drug target in Trypanosoma brucei. To better characterize its properties and guide drug design efforts, we have determined six new crystal structures of the enzyme, in various ligation states and conformations, and have carried out complementary molecular dynamics simulations. The results show a striking structural diversity of loops near the catalytic site, for which variation can be interpreted as distinct modes of conformational variability that are explored during the molecular dynamics simulations. Our results show that sulfate may, unexpectedly, induce full closure of catalytic site loops whereas, conversely, binding of inhibitor phosphonoacetohydroxamate may leave open a tunnel from the catalytic site to protein surface offering possibilities for drug development. We also present the first complex of enolase with a novel inhibitor 2-fluoro-2-phosphonoacetohydroxamate. The molecular dynamics results further encourage efforts to design irreversible species-specific inhibitors: they reveal that a parasite enzyme-specific lysine may approach the catalytic site more closely than crystal structures suggest and also cast light on the issue of accessibility of parasite enzyme-specific cysteines to chemically modifying reagents. One of the new sulfate structures contains a novel metal-binding site IV within the catalytic site cleft.

Molecular and biochemical characterization of novel glucokinases from Trypanosoma cruzi and Leishmania spp

Glucokinase genes, found in the genome databases of Trypanosoma cruzi and Leishmania major, were cloned and sequenced. Their expression in Escherichia coli resulted in the synthesis of soluble and active enzymes, TcGlcK and LmjGlcK, with a molecular mass of 43 kDa and 46 kDa, respectively. The enzymes were purified, and values of their kinetic parameters determined. The K(m) values for glucose were 1.0 mM for TcGlcK and 3.3 mM for LmjGlcK. For ATP, the K(m) values were 0.36 mM (TcGlcK) and 0.35 mM (LmjGlcK). A lower K(m) value for glucose (2.55 mM) was found when the (His)(6)-tag was removed from the recombinant LmjGlcK, whereas the TcGlcK retained the same value. The V(max)'s of the T. cruzi and L. major GlcKs were 36.3 and 30.9 U/mg of protein, respectively. No inhibition was exerted by glucose-6-phosphate. Similarly, no inhibition by inorganic pyrophosphate was found in contrast to previous observations made for the T. cruzi and L. mexicana hexokinases. Both trypanosomatid enzymes were only able to phosphorylate glucose indicating that they are true glucokinases. Gel-filtration chromatography showed that the GlcK of both trypanosomatids may occur as a monomer or dimer, dependent on the protein concentration. Both GlcK sequences have a type-1 peroxisome-targeting signal. Indeed, they were shown to be present inside glycosomes using three different methods. These glucokinases present highest, albeit still a moderate 24% sequence identity with their counterpart from Trichomonas vaginalis, which has been classified into group A of the hexokinase family. This group comprises mainly eubacterial and cyanobacterial glucokinases. Indeed, multiple sequence comparisons, as well as kinetic properties, strongly support the notion that these trypanosomatid enzymes belong to group A of the hexokinases, in which they, according to a phylogenetic analysis, form a separate cluster.

Enolase as a plasminogen binding protein in Leishmania mexicana

Enolase is a glycolytic and gluconeogenic enzyme also found on the surface of several eukaryotic and prokaryotic cells where it acts as plasminogen binding protein. Leishmania mexicana, one of the causative agents of Leishmaniasis, binds plasminogen and, in this parasite, enolase has been previously found associated with the external face of the plasma membrane. In this work, we show that the purified recombinant enolase has plasminogen binding activity indicating that, at the surface of the parasite, the protein may function as one of the plasminogen receptors. An internal motif (249)AYDAERKMY(257), similar to the nine amino-acid internal plasminogen-binding motif in Streptococcus pneumoniae enolase, is responsible for plasminogen interaction with the parasite enolase. Anti-enolase antibodies inhibited up to 60% of plasminogen binding on live parasites indicating that enolase act as a plasminogen receptor on the parasite. The fact that enolase acts as a possible plasminogen receptor in vivo makes this protein a promising target for therapy.